In a refrigeration unit such as an air conditioner, a refrigerator, and a cooling device for manufacturing, in some cases, an evaporator includes a plurality of paths (refrigerant flow passages in a heat exchanger). For example, in a refrigerant circuit shown in FIG. 43, a refrigerant compressed by a compressor 201 is condensed in a condenser 202, and passes through a receiver 203 to be sent to an expansion valve 204. A refrigerant decompressed by the expansion valve 204 is sent to a refrigerant flow divider 206 through a refrigerant conduit 205 and is divided by the refrigerant flow divider 206 to be sent to a plurality of paths of an evaporator 207. A low-pressure refrigerant is evaporated in the evaporator 207 and then returns to the compressor 201 through an accumulator 208. In a case where the evaporator 207 includes a plurality of paths as described above, the refrigerant flow divider 206 is connected to the expansion valve 204 through the refrigerant conduit 205. The refrigerant flow divider 206 uniformly divides the refrigerant decompressed by the expansion valve 204 into a plurality of paths of the evaporator 207. The refrigerant flow divider 206, as disclosed in Patent Document 1, has a predetermined volume and includes a space (refrigerant flow dividing chamber) for distributing a refrigerant. A flow dividing tube attachment hole used to connect the refrigerant flow dividing chamber and each path of the evaporator 207 is formed in the refrigerant flow divider 206. When decompressed in the expansion valve 204, refrigerant is converted to a low-pressure gas-liquid two-phase flow refrigerant before flowing into the refrigerant flow divider 206. Such a gas-liquid two-phase flow refrigerant is apt to create a plug flow or a slug flow containing big bubbles when it flows in the refrigerant conduit 205 which connects the expansion valve 204 and the refrigerant flow divider 206. When such a plug flow or a slug flow occurs, due to influence of gravity or the like, bubbles do not uniformly flow into each flow dividing tube attached to each flow dividing tube attachment tube, whereby the refrigerant becomes hard to be uniformly divided.
In order to realize the uniform division, in Patent Document 1, a throttle (path narrowing member) having a constant opening degree is disposed on the upstream side of the flow dividing tube attachment hole, so that a refrigerant becomes a spray state at a further downstream side than the throttle.
Meanwhile, refrigerant flowing into an expansion valve is a high-pressure liquid refrigerant, but due to a change in an operating condition of a refrigeration unit, bubbles may be contained in a refrigerant near an upstream side of an expansion valve, i.e., an outlet of a receiver or an outlet of a condenser. In this case, bubbles in the high-pressure liquid refrigerant are heated from the outside of a refrigerant conduit and so is expanded or united with each other while circulating in the refrigerant conduit. As a result, a plug flow or a slug flow occurs, so that liquid refrigerant and gaseous refrigerant alternately flow through the throttle. For this reason, the velocity and pressure of a refrigerant flow fluctuate, or the ejection velocity and ejection pressure of refrigerant ejected from the throttle to the refrigerant conduit fluctuate, so that a refrigerant flow noise is generated. Also, an expansion valve or equipment near the expansion valve such as a connecting conduit vibrates, causing a vibration noise. In order to reduce such a discontinuous refrigerant flow noise, in Patent Document 2, as a means for mitigating fluctuation in the velocity and pressure of a refrigerant flow, a throttle for decompressing a refrigerant flow is installed on the upstream side of a throttle. Also, in Patent Document 3, a turbulence generating portion for generating turbulence in a refrigerant flow is installed on the upstream side of a throttle. Also, in Patent Document 4, a throttle for decompressing a refrigerant flow is installed on the downstream side of a throttle.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-188869    Patent Document 2: Japanese Unexamined Patent Publication No. 2005-69644    Patent Document 3: Japanese Unexamined Patent Publication No. 2005-351605    Patent Document 4: Japanese Unexamined Patent Publication No. 2005-226846